Wide bitrate range scalability is now the latest trend in audio coding. A lot of efforts has been devoted to the development of algorithms for more efficient scalable audio coder that scales from very low bitrate. Scalable audio coding technique such as MPEG-4 Scalable Lossless coding (SLS) offers a unified solution for high-compression perceptual audio and high-quality lossless audio. SLS provides a fine-grain scalable extension of the well-known MPEG-4 Advanced Audio Coding (AAC) perceptual audio coder up to fully lossless reconstruction. Recently, the combination of SLS and AAC coder is renamed as "High Definition Advanced Audio Coding" (HD-AAC). It is observed that HD-AAC can be further improved at intermediate enhancement bitrate when the core bitrate is low. In this paper, a Perceptually Prioritized Bit-Plane Coding (PPBPC) is proposed. With this novel coding scheme, the bit-plane coding is performed with priorities according to the perceptual information of the signal to be coded. By using this low-complexity structure with trivial extra side information, the bit-plane coding for scalable audio can be implemented in a perceptually more efficient manner and the quality of the audio under aforementioned scenario is greatly improved.